Fast electron tomography: Applications to beam sensitive samples and in situ TEM or operando environmental TEM studies

Abstract

Electron Tomography (ET) is of greatest interest in studying nano- and biological materials since it gives access to 3D morphological, chemical and physical features. Even though ET techniques have been continuously improved in the last decades, they are still limited: lengthy time scales (tens of minutes) are generally needed for the tilt series acquisition prior to the volume reconstruction step. Such long exposures to a relatively intense electron beam lead to large electron doses received by the sample. This may promote extensive irradiation damage in the case of soft materials like polymers and bio-materials when they are not protected through dedicated sample preparation methods, and any tomographic reconstruction will then be meaningless. More importantly, the time constraints drastically limit 3D investigations during dynamic in-situ experiments where the sample rapidly evolves during the acquisition.We present here developments for acquiring tilt series of projections in very short time scales, readily down to a few seconds. After an outlook of possible ways to speed up the data acquisition in the bright field imaging mode (BF-TEM), strategies for the fastest methods in ‘step-by-step’ and ‘continuous tilt’ ET will be described. Applications of these procedures are presented on various systems, including metallic Pd nanoparticles deposited on alumina, and soft materials like polymer nanocomposites and biological matter. A special reference is made to fast operando nano-tomography performed on nanomaterials during their dynamic evolution. The feasibility of fast ET is exemplified by a calcination study of Pd catalysts supported by SiO2 at 400 °C and 500 °C under 4 mbar H2 in a dedicated Environmental Transmission Electron Microscope (ETEM).